Oscillatory and vibratory type mechanical separators have been commercially available for an extensive period of time for the purpose of separating solid materials and separating solid materials from liquid materials. One of the problems that arises is screen blockage, especially where solid materials are separated from liquid materials, such as in separation of drilling cuttings from the drilling mud that is utilized during the process of drilling oil wells. It has been determined that oscillatory and vibratory screens frequently become blocked by materials that are carried along with the drilling mud or other material. In fact, the liquid material passing through the screens often includes a small quantity of granular material and especially those liquids including various chemical and natural constituents, may have a certain degree of stringyness causing a considerable amount of the liquid or semi-solid slurry material to cling to the underside of the screen. When this occurs, the clinging material actually blocks at least a portion of the mesh of the screen and thereby substantially reduces the effectiveness of the screening operation. It is possible for the mesh openings of a typical drilling mud screen to become reduced in the order of 50 to 75 percent within a very short period of time. When this occurs, the commercial effectiveness of the screening or separating operation is severely reduced, thereby adding to the overall cost of the commercial operation with which it is associated. It is therefore desirable to provide means for cleaning the underside of the screen that accomplishes the primary screening function in order that the screen mesh openings will remain unblocked.